Hi Steve,
10-20 seconds depending on ambient air temperature and engine temperature (first run or warm/hot restart). I had a fascinating discussion about this with Henry Nelson, several years ago. Truthfully, we (pattern fliers or at least the CPA pilots) really don't need 'ABC' technology in our engines. The new new ringed YS short stroke confirms that. We just don't turn high enough rpms. I think OS discovered this, too, many years ago when they released two versions of the Hanno Special MKII; one 'ABC' and one ringed. Properly plated liners (OS had some peeling problems initially when they changed to Nikasil plating with their RF and SF engines) can easily last 1,000 flights. The Nelson liners can go 1,500 or more. I've never seen one peel, but the chrome will eventually wear off so you can see the brass showing.
Heat transfer in the aluminum liners is much better than the brass liners.
As far as piston expansion... One of my first YS .60FRs from way back in 1980 had the piston 'grow' in the sleeve so much it required some serious whacking with a hammer to get it to descend in the sleeve so I could get the engine apart. I still have the piston/sleeve and you cannot get the piston more than 1/2 way up the sleeve. Ys was experimenting with silicon content in their pistons back then. The piston 'growth' happened in my workshop over a two week period of down time (it was in my backup airplane).
Regards,
Will